1. Field of the Invention
The present invention relates to a light emitting device used for displays, sensors and the like.
2. Description of the Prior Art
A light emitting diode (LED) in the prior art will be described with reference to FIGS. 34 and 35. FIG. 34 is a schematic sectional view of a prior art LED of the so-called lens type, and FIG. 35 is a schematic sectional view of an LED of a reflection type.
A lens type LED 1000 shown in FIG. 34 has an LED chip 1001a emitting rays of red light; an LED chip 1001b emitting rays of green light; lead frames 1002a, 1002b, 1002c; light diffusible material 1003; light transmissible material 1004; and a lens surface 1005. The LED chips 1001a, 1001b are mounted on the lead frame 1002a, and electrically connected to the lead frames 1002b, 1002c by way of wires 1006a, 1006b, respectively. The LED chips 1001a, 1001b, and part of the wires 1006a, 1006b are sealed by means of the light diffusible material 1003 layered on the lead frame 1002a. The light diffusible material 1003, wires 1006a, 1006b, and the leading edge portions of the lead frames 1002a, 1002b, 1002c are integrally sealed by means of the light transmissible material 1004. The lens surface 1005 is formed by a method wherein the surface of the light transmissible material 1004 is formed in a convex shape on the light emitting surface side of the LED chips 1001a, 1001b.
In the lens-type LED 1000 having the above construction, rays of red light emitted by the LED chip 1001a and rays of green light emitted by the LED chip 1001b are diffused and mixed by the light diffusible material 1003, after which they are collected by the lens surface 1005 and radiated to the exterior. Thus, rays of light having different luminous colors can be radiated from the lens surface 1005 to the exterior with approximately the same luminous intensity distribution characteristics, and accordingly, rays of mixed light with no color-irregularity can be radiated to the exterior.
In the lens-type LED 1000 having the above construction, however, rays of light emitted by the LED chips 1001a, 1001b are sufficiently diffused by the light diffusible material 1003, and thereby they are uniformly radiated in all the directions from the surface of the light diffusible material 1003. Consequently, only part of the rays of light radiated from the surface of the light diffusible material 1003 reach the lens surface 1005. Since part of the rays of light emitted by the LED chips 1001a, 1001b are absorbed by the light diffusible material 1003, only part of the rays of light emitted by the LED chips 1001a, 100b can be radiated from the lens surface 1005. In the meanwhile, although the light diffusible material 1003 is substantially taken as a light source portion in the lens type LED 1000 having the above construction, it is larger than the LED chip and cannot be taken as a point light source, thus failing to perform sufficient optical control by the lens surface 1005. Accordingly, the lens-type LED 1000 in the prior art having the above construction presents a problem that it is significantly poor in collecting efficiency and cannot obtain a high frontal luminance. For example, a lens type LED having a structure shown in FIG. 34, which is prepared such that two LED chips are used to obtain sufficient color mixing, exhibits a frontal luminance being about 1/20 that of a lens-type LED which is sealed only by a light transmissible material without any light diffusible material.
A reflection type LED 1100 shown in FIG. 35 has an LED chip 1101a emitting rays of red light; an LED chip 1101b emitting rays of green light; lead frames 1102a, 1102b; a light transmissible material 1103; and a concave surface-like reflection surface 1105 provided to face the light emitting surface of the LED chips 1101a, 1101b. The LED chips 1101a, 1101b are mounted on the lead frames 1102a, 1102b, and are electrically connected to respective lead frames (not shown) by means of respective wires (not shown). The LED chips 1101a, 1101b, the leading edge portions of the lead frames 1102a, 1102b, the leading edge portions of the lead frames (not shown) and the wires (not shown) are integrally sealed by the light transmissible material 1103. The concave surface-like reflection surface 1105 is formed on a convex surface of the light transmissible material 1103.
In the reflection-type LED 1100 having the above construction, the whole luminous flux of red light emitted by the LED chip 1101a and the whole luminous flux of the green light emitted by the LED chip 1101b are almost entirely reflected from the concave surface-like reflection surface 1105 and radiated to the exterior. Accordingly, the reflection-type LED 1100 having the above construction can obtain a frontal luminance higher than that of the prior art lens-type LED 1000 shown in FIG. 34.
In the reflection-type LED 1100, however, it is unclear what structure is most suitable for effectively mixing rays of red light emitted by the LED chip 1101a and rays of green light emitted by the LED chip 1101b. In addition, it may be considered a structure of integrally sealing the LED chip 1101a and the LED chip 1101b with a light diffusible material; however, this structure presents a problem in shielding rays of light reflected from the concave surface-like reflection surface 1105 by the light diffusible material.